1. Technical Field
The present invention relates to an automotive air conditioning system, and more particularly, to an automotive air conditioning system which includes a refrigerant compressor with an externally controlled variable displacement mechanism.
2. Description of the Prior Art
Generally, in an automotive air conditioning system, a refrigerant compressor is intermittently driven by an automobile engine through an electromagnetic clutch which is associated with the compressor in response to changes in the demand for air conditioning in an automobile passenger compartment so that the temperature of air in the auto passenger compartment is maintained at the required temperature. According to Japanese Patent Application Publication No. 55-148614, when the amount of demand for acceleration of the automobile is equal to or greater than a certain value, operation of the refrigerant compressor is stopped by means of deenergization of the electromagnetic clutch so that the power output from the automobile engine is effectively used for driving the automobile. However, this manner of stopping operation of the refrigerant compressor can cause inadequate air conditioning in the automobile passenger compartment because no air conditioning is carried out in the automobile passenger compartment due to the stopping of the operation of the refrigerant compressor.
In order to overcome this drawback, Japanese Patent Application Publication No. 57-195884 discloses an automobile air conditioning system which includes a refrigerant compressor with an externally controlled variable displacement mechanism. According to this Japanese Patent Application Publication, when the amount of demand for acceleration of the automobile is equal to or greater than a certain value, the capacity of the refrigerant compressor is forcibly reduced to the minimum displacement to produce extra power which is shared with driving the automobile. However, when the capacity of the refrigerant compressor is forcibly reduced to the minimum displacement in a smaller displacement stage, a negligible amount of extra power is produced and the air conditioning in the automobile passenger compartment is inadequately carried out. Therefore, when the amount of demand for acceleration of the automobile is equal to or greater than a certain value in the smaller compressor displacement stage, the capacity of the compressor is merely uselessly controlled. Furthermore, as shown in FIG. 1, when the capacity of the refrigerant compressor is forcibly reduced to the minimum displacement in a larger displacement stage, a sufficient amount of extra power cannot be instantly obtained in comparison with the stopping of the operation of the compressor by means of deenergization of the electromagnetic clutch as described above. Therefore, when the amount of demand for acceleration of the automobile is equal to or greater than a certain value in a larger compressor displacement stage, a reduction of the accelerating performance of the automobile due to operation of the compressor is not quickly adequately compensated.